An inkjet franking machine is disclosed in U.S. Pat. No. 5,083,153. Inkjet printing renders franking machines highly versatile, in particular when it is question of printing on the articles for mailing postal indicia comprising both variable characters, such as the numerical values of an amount of postage, and arrangements of colours such as those of advertizing logos.
Due to the dimensions of the indicia to be printed and those of the bars (or casings) of ink ejection nozzles currently available on the market, it has proved that printing of such indicia can be carried out at the present time under acceptable economic conditions, only from two offset rows of ejection nozzles. The printing faults (particularly connection in the median part) due to the relatively imprecise positioning of these rows (however, Applicants have proposed in French Applications FR 2 724 591 and FR 2 724 592 appropriate methods for adjusting in situ before printing in order to obtain a perfect alignment of the nozzles of the two boxes), accentuated by the shocks provoked by the conveyor rollers on the article for mailing during transport thereof, certainly raise acute problems in mail processing. In effect, in this particular technical domain, the indicia includes critical postage data such as the amount of franking which represents a monetary value and no fault affecting this value, however small, can be accepted by the Postal Service. Moreover, with the introduction of so-called “intelligent” indicia, integrated coded information, there is the problem of authentication and checking of this information. In effect, verification and validity of the indicia lies with the recognition of this coded information as well, possibly, as other information shown clear on the indicia (date or machine number for example) and an error in reading resulting from misaligned connections may have damaging consequences as to the validity finally recognized of the article for mailing.
It is an object of the present invention to overcome the problems set forth hereinabove by proposing an improved printing process which avoids, at least at the level of the critical postal data, misaligned connections of the ejection nozzles of the printing device of an inkjet franking machine. One object of the invention is to eliminate such misaligned connections without notably increasing the structure of the printing device. Another object of the invention is to facilitate subsequent recognition of the critical postal data by the Postal Service.